Drywall is a common building material comprising a core of gypsum located between two cover sheets. Drywall has been used globally in the construction of interior walls and ceilings for many years and is present in substantial quantities in most modern homes throughout the world. It is therefore essential that drywall not pose environmental problems.
In 2006 an estimated 300 to 500 million pounds of drywall manufactured in China (“Chinese Drywall”) were imported into the United States in part due to increased demand caused by rebuilding efforts following the active hurricane seasons in 2004 and 2005. Soon after, the US Consumer Product Safety Commission began receiving complaints from residents of newly dry-walled structures in more than 20 states that the Chinese Drywall was causing unpleasant sulfurous odors and premature HVAC system failures. The HVAC system failures were from premature corrosion of copper coil assemblies and other metal components. Much or all of the installed defective Chinese Drywall, which is apparently the source of the corrosion, may have to be removed to abate these problems. In order to contain this massive undertaking and to control its economic costs, it is important to be able to easily and accurately identify the problematic drywall which may need to be removed.
The corrosion product observed on failed or failing HVAC copper coil assemblies varies from a black discoloration to a loosely adhered black scale. The darkened surface scale has been determined by energy dispersive x-ray analysis to consist of a material containing copper, sulfur and oxygen in varying proportions, consistent with corrosion of the copper caused by exposure to hydrogen sulfide (H2S) gas. In the presence of H2S, copper reacts to form a mixture of copper sulfide (Cu2S) and copper oxides (Cu2O and CuO) which correspond to the black discoloration and loosely adhered black scale.
Low concentrations of H2S have been detected in closed chamber testing of defective Chinese Drywall and higher levels are observed when the defective drywall is crushed into finer particles. Gaseous carbonyl sulfide (OCS) and carbon disulfide (CS2) have also been detected in closed chamber testing of defective Chinese Drywall. In the presence of moisture, OCS hydrolyzes to form H2S and OCS is reported to corrode copper at a rate similar to the rate of corrosion caused by H2S. The source of these sulfur gases is believed to be particles of elemental sulfur, possibly originally present in the mined gypsum mineral, and retained in defective Chinese Drywall as an impurity.
Existing methods for identifying defective Chinese Drywall involve destructive testing of the drywall. For example, multiple samples are cut from various locations in the suspected drywall installation and submitted to a laboratory for determination of the presence of elemental sulfur or testing in a closed chamber in the presence of copper. The determination of the presence of elemental sulfur may be performed by high performance liquid chromatography, mass spectrometry, or Fourier transform infrared analysis.
Therefore, if a device and method were provided for detecting the presence of H2S, OCS, or other corrosive materials in drywall simply, inexpensively and with relative dispatch, an important contribution to the art would be a hand. If the device and method could be used on already installed drywall without removing or cutting test samples from the drywall, a particularly important contribution to the art would be a hand. Finally, if the device and method could be made tamperproof to insure that reliable results are obtained in a simple and economic way, the problem of reliably and non-destructively identifying defective Chinese Drywall and drywall containing other corrosive materials, would be solved. The present invention meets all of these objectives.